1. Field of the Invention
The present invention relates to determining whether thrombolysis therapy would be beneficial to an acute ischemic stroke patient, and more particularly, to methods and apparatuses for making such a determination.
2. Background of the Related Art
Ischemic strokes are the third leading cause of death after cardio-vascular diseases and cancers. In the United States alone, strokes affect over 750,000 patients each year, among whom one-third will be permanently disabled. Thus, strokes represent one of the leading causes of disability.
Viability of the cerebral tissue depends on cerebral blood flow. During a stroke, a portion of brain tissue known as the ischemic lesion is deprived of sufficient blood flow due to an arterial occlusion (blood clot). The ischemic lesion includes two parts: the infarct and the penumbra. The infarct comprises brain tissue in which blood flow is so drastically reduced that the brain cells do not recover. The penumbra surrounds the infarct and corresponds to a transitional zone in which brain cells are endangered, but not yet irreversibly damaged.
A major difference between penumbra and infarct relates to cerebral perfusion autoregulation. Complex autoregulation processes ensure both the adjustment of cerebral blood flow to local neuronal activity and cerebral blood flow stability despite changes in systemic arterial pressure. Brain vascular autoregulation notably allows for a vascular dilatation when the systemic pressure tends to lower, in order to keep a constant cerebral blood flow. This vascular dilatation leads in turn to an increased cerebral blood volume, at least in salvageable penumbra. In infarcted cerebral gray matter, autoregulation mechanisms are altered, and both cerebral blood flow and cerebral blood volume are diminished.
Early after a cerebral arterial occlusion occurs, reversible inhibition or penumbra occurs in the territory of cerebral tissue usually perfused by the affected artery. With time, irretrievable infarction, however, progressively replaces the penumbra. The replacement rate varies according to the collateral circulation level.
Thrombolysis therapy using blood clot dissolution drugs has been introduced to save ischemic but viable cerebral tissue. The application of this therapy relies on the time interval between the onset of symptomatology and the native cerebral CT findings.
However, if thrombolysis therapy is used on a patient where extensive oligemia in the territory of an occluded cerebral artery, where there is limited penumbra area, the therapy would yield little to no benefit and even increases the risk of intracranial bleeding.